The increasing cost of fossil fuel and environmental concerns have stimulated world-wide interest in developing alternatives to petroleum-based fuels, chemicals, and other products. Biomass materials are a possible renewable alternative.
Lignocellulosic biomass includes three major components. Cellulose, a primary sugar source for bioconversion processes, includes high molecular weight polymers formed of tightly linked glucose monomers. Hemicellulose, a secondary sugar source, includes shorter polymers formed of various sugars. Lignin includes phenylpropanoic acid moieties polymerized in a complex three dimensional structure. The resulting composition of lignocellulosic biomass is roughly 40-50% cellulose, 20-25% hemicellulose, and 25-35% lignin, by weight percent.
No cost-effective process currently exists for efficiently converting cellulose, hemicellulose, and lignin to components better suited for producing fuels, chemicals, and other products. This is generally because each of the lignin, cellulose and hemicellulose components demand distinct processing conditions, such as temperature, pressure, catalysts, reaction time, etc. in order to effectively break apart its polymer structure.
A need exists for a method for converting biomass to oxygenated compounds suitable for bioreforming processes, such as Aqueous-Phase Reforming (APR) and hydrodeoxygenation (HDO). Ideally, the method would convert biomass to carbohydrates, such as starches, saccharides, sugars and sugar alcohols, which are desirable feedstock for bioreforming processes.
Existing methods for converting biomass to usable feedstock are not sufficient to meet the growing needs of bioreforming processes. Hot water extraction of hemicelluloses from biomass has been well documented, but the sugars produced by hot water extraction are unstable at high temperatures leading to undesirable decomposition products. Therefore, the temperature of the water used for hot water extraction is limited, which can reduce the effectiveness of the hot water extraction.
Additionally, studies have shown that it is possible to convert microcrystalline cellulose (MCC) to polyols using hot, compressed water and a hydrogenation catalyst (Fukuoka & Dhepe, 2006; Luo et al., 2007; and Yan et al., 2006). Typical hydrogenation catalysts include ruthenium or platinum supported on carbon or aluminum oxide. However, these studies also show that only low levels of MCC are converted with these catalysts. Selectivity toward desired sugar alcohols is also low. Therefore, a process for converting biomass to polyols for further processing to fuels, chemicals, and other products would be beneficial.
APR and HDO are catalytic reforming processes that generate hydrogen and hydrocarbons from oxygenated compounds derived from a wide array of biomass. The oxygenated hydrocarbons include starches, mono- and poly-saccharides, sugars, sugar alcohols, etc. Various APR methods and techniques are described in U.S. Pat. Nos. 6,699,457; 6,964,757; 6,964,758; and 7,618,612 (all to Cortright et al., and entitled “Low-Temperature Hydrogen Production from Oxygenated Hydrocarbons”); U.S. Pat. No. 6,953,873 (to Cortright et al., and entitled “Low-Temperature Hydrocarbon Production from Oxygenated Hydrocarbons”); and U.S. Pat. Nos. 7,767,867 and 7,989,664 and U.S. Application Ser. No. 2011/0306804 (all to Cortright, and entitled “Methods and Systems for Generating Polyols”). Various APR and HDO methods and techniques are described in U.S. Patent Application Ser. Nos. 2008/0216391; 2008/0300434; and 2008/0300435 (all to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); U.S. Patent Application Ser. No. 2009/0211942 (to Cortright, and entitled “Catalysts and Methods for Reforming Oxygenated Compounds”); U.S. Patent Application Ser. No. 2010/0076233 (to Cortright et al., and entitled “Synthesis of Liquid Fuels from Biomass”); International Patent Application No. PCT/US2008/056330 (to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); and commonly owned co-pending International Patent Application No. PCT/US2006/048030 (to Cortright et al., and entitled “Catalyst and Methods for Reforming Oxygenated Compounds”), all of which are incorporated herein by reference.
Biomass must be deconstructed to less complex oxygenated compounds prior to use as feedstock for bioreforming processes. There remains a need for cost-effective methods for separating biomass into streams suitable for use in APR, HDO and other bioreforming processes.